Straight from Vox:
Elon Musk has a vision. All it’ll take is a lot more chance, a fortune, and a really, really ridiculously large spaceship.
Musk made his impassioned and thorough claim for space colonization at an event with SpaceX, his private spaceflight company. “Someday soon, there will be an extinction event on Earth,” Musk said. So we can sit around and wait for that to hit. “Or, the choice is to become a spacefaring species.”
If humans sent, say, 10,000 flights in all, we could presumably assemble a self sustaining civilization on Mars would take 20 to 40 years in all, given the launch window. Musk implied that we might one day power a Martian civilization with geothermal or solar panels: “ If you’ve got energy on Mars, you’re going to have water because there’s enormous amounts of ice.”
Musk hinted at the chance of terraforming Mars — releasing enormous amounts of carbon dioxide to warm the planet and bring water that was liquid back, making it habitable for people. If we could warm upwards Mars, we might have a thick atmosphere and warm oceans,” he said.
More juicy bits are at the source.